Axially adjustable steering column assemblies for vehicles are designed to extend and retract axially toward and away from the driver, and to be fixed in a desired axially extended or retracted position. A common arrangement uses an outer tube or jacket with one end oriented to the steering wheel and a distal end adapted to receive an inner tube or jacket, with appropriate clearance between the telescoping jackets. A desirable arrangement provides smooth, low effort telescoping extension and retraction, free of perceptible lash, or looseness, while providing high stiffness to resist deflection when a moment force is applied. A problem in practice pertains to the conflicting requirements of high vertical and lateral stiffness with low telescoping efforts. The amount of lash and stiffness reduction can increase with extension of the column, or with decreased telescoping effort from too large a clearance between the jackets. Variances in telescoping tolerances which adversely affect smooth operation of column extension and retraction are caused by fluctuations in tube stock, warping from welding operations such as welded attachment of brackets to the tubes, and random moment forces as applied, for example, through an attached steering wheel. These variances in telescoping forces also adversely affect the energy management function of steering columns designed to collapse in the event of a crash. A universal solution which reduces or eliminates lash and increases stiffness from all three of these sources while producing smooth, low effort telescoping operation would be desirable.
One approach involves the use of a sleeve between the opposing surfaces of the telescoped jackets. Such sleeves have been made of metal or plastic for interference fit between the opposing surfaces of the jackets, with surface-to-surface contact with one or both of the jackets, and in some versions localized contact with the surface of the other jacket. This is accomplished by projections on one side of the sleeve which contact the opposing jacket surface. This localized contact, while effective in reducing telescoping effort, does not eliminate lash, and generally reduces vertical stiffness, particularly when a bending moment is placed on the column assembly. Sleeves which fit directly over the inner jacket in surface-to-surface contact can transmit imperfections in the outer surface of the inner jacket, producing excess friction. A steering column assembly which provides both the correct amount of frictional resistance to axial movement of the telescoped members, with no lash, and which have high vertical stiffness is desired.